1. Field of the Invention
The present invention relates generally to a method and apparatus for wavelength selective optical switching and multiplexing/demultiplexing, and more particularly to a wavelength selective optical switch providing improved transmission capacity.
2. Description of the Prior Art
The explosive growth of telecommunication and computer networking, especially in the area of the Internet, has created a dramatic increase in the volume of data traffic worldwide, which has placed an increasing demand for communication networks to provide more and more bandwidth. To meet this demand, fiber optic (light wave) communication systems have been developed in order to harness the enormous usable bandwidth (tens of tera-Hertz) of a single optical fiber transmission link. Because it is not possible to exploit all of the bandwidth of an optical fiber using a single high capacity channel, wavelength division-multiplexing (WDM) fiber optic systems have been developed to provide transmission of multi-carrier signals over a single optical fiber thereby increasing the bandwidth of the fiber dramatically. In accordance with WDM technology, a plurality of concurrent signals with different wavelengths are superimposed and transmitted over a single fiber. WDM technology takes advantage of the relative ease of signal manipulation in the wavelength, or optical frequency domain, as opposed to the time domain. In WDM networks, optical transmitters and receivers are tuned to transmit and receive on a specific wavelength, and many signals operating on distinct wavelengths share a single fiber.
Wavelength multiplexing devices are commonly used in fiber optic communication systems to generate a single multi-carrier signal, in response to a plurality of concurrent signals having different wavelengths received from associated sources or channels, for transmission via a single fiber. At the receiving end, wavelength demultiplexing devices are commonly used to separate the composite wavelength signal into several original signals of different wavelengths.
Dense wavelength division multiplexing (DWDM) devices provide multiplexing and demultiplexing functions in specific wavelength ranges. Important design criteria for a DWDM device include a large number of channels, narrow channel spacing, low inter-channel cross talk, low insertion loss, low polarization dependency, compactness, environmental stability, and low manufacturing cost.
The explosive growth of telecommunications, computer communications and the internet has placed increasing demand on national and international communication networks. The worldwide growth in the volume of data transmitted through existing communication systems has created a demand for a multi gigabit capacity transmission network with high efficient crossconnecting. A multi-channel switch that is capable of accommodating switching tasks from a large number of fiber channels to another large number of fiber channels is needed to meet this demand. A critical component in any communication system is the switch by which the communication system uses to cross connect between two or more signal carrying channels. In fiber optic communication systems, an optical switch is a device that is capable of rapidly switching selected data carrying beams from one of the optical fibers of an input fiber array to an optical fiber of an output fiber array. Therefore an optical switch with a high speed, low transmission loss and high reliably is desirable.
Conventional optical switch designs envision the use of a number of fixed fibers in conjunction with an array of moveable fibers which are either translated or rotated in to optical alignment with one of the fixed fibers by mechanical means. Complex and cumbersome mechanical mechanisms are currently used in order to perform optical switching. Furthermore, switches are currently only able to align one moveable fiber with one fixed fiber at a time.
What is needed is a dense wavelength division multiplexing (DWDM) device having capability of wavelength selective switching.
What is needed is a switching system that is capable of simultaneously aligning a group of signal carrying fibers with another group of signal carrying fibers.
What is also needed is a DWDM device that accommodates large transmission capacity while being small, lightweight, immune to temperature variation and stress-induced instability, and inexpensive to produce.
It is therefore an object of the present invention to provide a dense wavelength division multiplexing (DWDM) device having capability of wavelength selective switching.
It is also an object of the present invention to provide a DWDM device that accommodates large transmission capacity while being small, lightweight, immune to temperature variation and stress-induced instability, and inexpensive to produce.
Briefly, a presently preferred embodiment of the present invention provides an optical cross switch device for selectively switching light beams between a plurality of fiber optic elements. The device includes: an input fiber mounting assembly for securing at least one input fiber terminating in a fiber end for radiating an associated input light beam; collimating means for collimating the input light beam; focusing means for focusing light beams incident thereon; an output fiber mounting assembly for securing at least one output fiber terminating in an output fiber end for receiving an associated light beam; and at least one mirror unit having at least one reflective element for selectively redirecting an associated one of the collimated input light beams toward an associated selected one of the output fiber ends via the focusing means. Wherein the focusing means includes a lens and an auto-focusing and tracking mechanism operative to focus the redirected light beams. The reflective element being selectively rotatable about two substantially perpendicular axes for redirecting light beams incident thereon, wherein the reflective element is flexibly mounted on a substrate such that the angle of rotation of the reflective element is controlled by the application of voltage between a portion of the reflective element and a portion of the substrate. Alternatively, the focusing means may include an array of focusing lenses, and the collimating means may include an array of collimating lenses.
In one accordance with one aspect of the present invention, the device functions as a wavelength selective cross switch and add/drop multiplexer wherein the input light beam is a multi-channel beam. In accordance with one aspect of the present invention, the device further includes a transmissive grating for diffracting the multi-channel beam into a plurality of spatially separated single channel beams; and at least one mirror unit having at least one reflective element for selectively redirecting an associated one of the single-channel beams toward a selected one of the output fiber ends via the focusing means. In accordance with one aspect of the present invention, the transmissive grating includes a diffractive element formed from a photosensitive medium such as a photo-polymer material.